One example of a conventional method of cleaning the surface of a compound semiconductor and growing the compound semiconductor thin film is as follows:
preparing a ZnSe substrate; PA1 placing the ZnSe substrate inside an apparatus, which is highly evacuated at 10.sup.-9 Torr; and PA1 heating the substrate to 440.degree.-650.degree. C., thus removing contaminants from the surface of the substrate and then growing a ZnSe thin film on the substrate.
This method is mentioned, for example, in the Journal of Vacuum Science and Technology B, 9: 4 (1991), pp.1934-1938.
In this conventional method, however, the ZnSe thin film, grown on the substrate surface by a molecular beam epitaxy (MBE) method or a metal-organic chemical vapor deposition (MOCVD) method, is electrically and optically lowered although contaminant on the ZnSe substrate surface is removed by heating the surface at 440.degree.-650.degree. C. This is because the temperature (440.degree.-650.degree. C.) of the conventional method is higher than the growth temperature (about 150.degree.-400.degree. C.) of the ZnSe thin film grown by an MBE method or an MOCVD method.
A dry etching method of irradiating a hydrogen radical beam onto the surface of a compound semiconductor is disclosed in Japanese Published Patent Application No. Hei 2-267938 as a method of cleaning the compound semiconductor surface and growing the compound semiconductor thin film. However, in this method, the crystallinity of the compound semiconductor thin film regrown on the compound semiconductor is not substantial enough to be useful.